Prior electrically driven impact tools have utilized low amounts of energy and have been used in applications, such as for driving small nails and staples, loosening and tightening nuts or seating deformable fasteners, such as small brass and copper rivets. Substantially all high energy impact tools, particularly those which have been sufficiently light to be hand used, have operated on compressed air. However, such air tools have required, for supply of air through hoses to the tools, a high volume air compressor which is stationary or requires a cumbersome trailer or similar support, for transportation and location at the site at which the tool or tools are to be used. The additional pneumatic equipment, such as pressure regulators, lubricators, filters and the like, complicate the supply mechanism. Electrically driven impact tools which are hand held and especially those which are adaptable to nail driving purposes, are quite attractive in view of the fact that, at almost all construction sites, electrical power is normally available in substantially any desired quantity.
It has been proposed, in the James E. Smith and James D. Cunningham U.S. application Ser. No. 580,246, now U.S. Pat. No. 4,042,036, to provide an electrical impact tool having a specific application to a nail driving tool by utilizing one stationarily mounted and one pivotally mounted motor and rotating flywheel assembly, with the stationarily mounted, rotating flywheel being adjacent one side of a ram and the opposite side of the ram being engaged by the pivotally mounted, rotating flywheel. Movement of the latter into engagement with the ram is produced by a movable nose piece which is pushed into engagement with the work. Lateral movement of the latter is used to push the ram against the stationarily mounted, rotating flywheel, which requires that the ram have sufficient lateral play to accommodate this movement, with the result that undue wear on one side of the ram is produced. Often, an inadequate force is produced to move the pivoted, rotating flywheel into engagement with the ram. Thus, this force may vary with different operators and also in accordance with the position in which the nail is to be driven, i.e. between a downwardly driven nail, an upwardly driven nail and a laterally driven nail, for which the gravitational force of the weight of the tool may vary from assisting the movement of the nose piece to opposing it. Thus, the force which the operator must supply differs considerably. Other problems have arisen in connection with the practical application of such a construction to a tool for driving nails, including erratic starting of the ram, undue wear at the impact points of the rotating flywheels, the tendency for the production of forces which deflect the ram laterally, absence of equalization of the engagement forces of the two flywheels, accidental starting of the ram by the stationarily mounted, rotating flywheel, difficulty in disengagement of the ram from the stationarily mounted, rotating flywheel, a tendency for the rotating flywheels to "grab" the sides of the ram, difficulties in producing a smooth acceleration of the ram and undue losses in power effectively transmitted to the ram. Other problems included difficulties in returning the ram to its initial position, including localized elongation of a coil spring and frequent breakage of a rubber cord attempted to be utilized for that purpose. As a result, there has been difficulty in consistent reproduction of the desired nail driving characteristics. The electrically driven impact tool of this invention is designed to overcome the foregoing difficulties, as well as to provide additional novel features.